Process for electroplating strip steel



J. S.- NACHTMAN vPROCESS goa ELECTROPLATING STRIP STEE Dec. 16, 1941.

Filed Feb. 25, 193'?A Y 2 SheeSv--Shee'l 1 Dec- 16, 1941 J. s. NACHTMAN 21,266,330

PROCESS FOR ELECTROPLATING STRIP STEL Filed Feb. 25, 1937 2 Sheets-Sheet 2 I 'U72' Mci/mfp,

. cludes an electrical Patented Dec. 16, 11941 i UNITED" STATES vPATENT OFFICE l um vPRCESS FOR ELSETCFOPIATING Sm John s. Nsenmn, Beaver, rs. `Application February 25, 1937, Serial No. 127,176 Claims.l (Cl. 20d-28) This invention relates to a new and improved method of producing tin-plated ferrous metal stock and is particularly directed to the production of improved tin coatings upon steel stock in the form of strips, sheets or wire oi extensive length.

A principal object of the invention is the production of improved tin-plated ferrous metal, and especially the production of tin-plated steel strip stock which is more suited to the manufacture of cans or containers for food products than the tin-plated stock heretofore available.

A further object of the invention is to provide a tin-plated ferrousnetal than the so-called tin coating method. Another object of the invention is the provision of a method for` therapid and economical plating of steel or other ferrous metal in the form of strips or sheets of greatly extended length which may be coiled or reeled.

It is important that cans or containers. such as for food products. shall be highly rust resistant and free from surface defects and pinholes, whereby the plated product is given a longer life and the contents of the containers are protected against deterioration and contamination; and it is also desirable that the plated product have a lustre finish exterior, rendering it more attractive.

It has been found that the above-mentioned objects and other desirable advantages may be attained bythe method of the invention which comprises electro-plating the base stock with a ferrous or non-ferrous metal or alloy and thereafter electroplating the stock with tin. It is further particularly advantageous to subject the plated stock after the final plating to a temperature suflicient to alloy the nal plating with the earlier plating. The plated stock may also advantageously he subjected to a heating operation before the final plating, whereby the earlier plating or platings are caused to alloy with the fer- :ous metal base.

It is desirable to subject the base metal to thorough cleaning before submitting it to the plating operations. Preferably this cleaning incleaning operation whereby the base stock is passed in immediate succession through a plurality of electrical pickling baths in one of which the base stock is the cathode and hot more economical method for the production of heated to effect alloying in order to improve the quality and appearance of the coating. The preliminary plating may be effected. with any electrolytically depositable ferrous or nonferrous metal or alloy of such metal, preferably including at least one metal other than tin. Among the metals which may be used in the first plating are copper, nickel, chromium, cobalt, tungsten, iron and the like or alloys thereof such as copper-tin; copper-nickel, nickel-iron, nickelcobalt, and the like.

The base metal stock may in general be any suitable ferrous metal in sheet, strip wire or other extended form. Thus, :when I speak ci strip," I have reference to any suitable extended form such as previously mentioned. Rolled steel is particularly suitable and may be utilized in hot rolled condition, or after cold rolling or annealingor both. summarized brieyfor obtaining the same iinal quality product in the case of hot rolled stock, I prefer the following sequence of operations: (1) pickle toremove scale and oxides; (2) wet mechanically clean the strip to remove particles, nlm, etc., left by the pickle; (3) plate with an under coat of metal; (4) roll the strip to reduce it to proper gauge, thus hardening it; (5) anneal the strip to remove the hardness produced in (4) above and to alloy the metal under coat to the base strip; (6) clean the annealed strip for further plating; (7) plate with a metal having a low melting point such as tin or an alloy such as terne; (8) heat the strip to fuse the last applied coating and to alloy such coating with the metal under coating. It is apparent that the process can be applied to the strip in any condition between hot rolled and completely cold rolled.

For the purpose of illustration a specific embodiment of the principles of the invention will be more particularly described with reference to the accompanying'drawings which are diagrammatic representations of a typical embodiment of the invention.

In the drawings: o

Fig. 1 shows the cleaning and preliminary plating of ferrous metal strip;

Fig. 2 shows the steps of rolling the preliminarily plated strip to gauge and alloying the plating with the base metal; Y

Fig. 3 shows further cleaning and tin-plating of the strip; and,

Fig. 4 shows the steps oi alloying the tin plating with the previous plating and subjecting the strip to a smoothing or gauging operation.

lo The practice of my invention will be partichot rolled strip steel. The strip steel to be plated is unwound from a payoff reel III from which the strip II is pulled, by pull rolls at the different stations along the line, as hereinafter explained.

The strip II passes in succession through tanks I2 and I3, each of which contains a pickling electrolyte which may be like that described in my Patent No. 1,950,689 or may be a neutral salt. such as ammonium iluoride or sodium nitrate. In the pickling tank I2, the pickllng is cathodic and in tank I3 itis anodic.

In the case of the pickling tank I2 the positive side of generator G is connected to plates I2a submerged in the electrolyte, and the negative side of the generator ls connected to one or both of the metallic guide rollers I2b also submerged in the electrolyte and over which the strip II passes.

From the tank I2 the strips II pass over a guide roller I2c into a tank I3 where the positive side of the generator G is connected to one or more of the guide rollers I3b and the negative side is connected with the plates I3a submerged in the electrolyte.

While generators G are shown for purpose of illustration, any suitable source of current for this purpose may be employed. This treatment is especially eilicacious in producing chemically clean surfaces on the strip or strips II for electro-depositing or plating by. removing all oxides rolled into the strip by the hot rolling process.

From the tank I3 the strip stock II passes over a guide roller I3c and there is subjected to a mechanical cleaning. This mechanical cleaning may be performed by the apparatus I 4 which may comprise rotary brushes Ila which will contact both sides of the strip stock II and also spray devices Hb arranged for spraying either water or steam on the surfaces of the strip stock. However, other forms of mechanical cleaning may be found desirable. i

From the brushing and spraying apparatus I4,

the cleaned strip passes over a roll II that directs it through the plating tank I6 containing any suitable electrolyte according to the metal or alloy to be plated, but which, for the plating of copper, may consist of copper cyanide, sodium cyanide, sodium sulphite and water. 'Ihe strip is electrically connected with the negative pole of a direct current generator and is therefore the cathode. The copper anodes I'I above and below the strip. as shown, are connected to the positive side of the direct current generator, and thus plate each side of the strip.

It is preferred in the present process to only plate a thin or ash coating at the tank I6, which is usually suflicient for the purposes .of the invention. However, heavier coatings may be plated and for some purposes may be desirable. i From the plating tank or station I6, the strip passes from a roll I8, first to a water rinsing tank I3 containing cold water and then to and through a tank 23 containing hot water which, due to the rapid evaporation of the hot water. may suililciently dry the strip stock. However, if found desirable, a drier, not shown, but which may be thesame asthedrier 36 showninmyU.S.Pat ent No; 1,991,817, may be employed. From this drying step the strip stock II passes over drums 2I by which the pulling action on the strip is effected.

ReferringtoFig.2itwillbeseenthatthecop `perplatedstripstockIIispassedtooneormore cold rolling machinesV 23, whose construction need not be described in detail, by which it is cold rolled to the desired thickness. The strip stock I I, leaving the rolling rolls 23a, is kept under tension by pinch rolls 24 from which it is passed to a vertical furnace 25 by feed rolls 26 which eliminates marking or scratching the stock and conserves horizontal space in the plant. In such furnace 26 reducing atmosphere is maintained and the strip stock is subjected to a temperature approximately the melting point of the metal deposited at I6, but below the melting point of the base metal, which in the case of copper is about 1950" F. This heat treatment produces an alloy between the contiguous surfaces of the plating metal and of the base strip stock II, thereby at least providing three distinct layers. consisting of the base metal, the alloy and the plated metal, and rendering the plated strip stock almost free from pinholes when thin plating is done at I6. Of course, it is understood that heavier plating would eliminate all pinholes. Satisfactory results may be obtained by usinglower temperatures in the furnace 25. The temperature is selected `according to the depth of alloying desired. The higher the temperature, the greater the alloy depth.

. From the furnace the strip passes between rolls 21 and is delivered to pulling drums 28 (corresponding to the similar drums 2I of Fig. 1) by which the strip is pulled onward.

After the above-described three layer alloying step the plated strip stock is subjected to a cleaning treatment, shown by way of example, by first passing it through the cleaning tank 30 containing. preferably, an alkaline bath and, then, to the mechanical cleaner 3| comprising a water spray and brushing means similar to the cleaner I4 in Fig. 1. After being thus cleaned, the strip may be next subjected to a brightening dip in tank 32 containing chromic acid and sulphuric acid, and after being etched it is again water sprayed and brushed by apparatus 33 similar to 3|. The plated strip stock is now prepared for the tin-electro-plating bath to which it is next subjected for tin plating.

The tin electrolyte bath is contained in a tank 34 of usual construction andsimilar to the tank I6 oi' Fig. 1. 'I'he strip is the cathode and is therefore connected with the negative side of the generator and there are tin anodes 35 above and below the strip, as shown, connected to the positive side of the generator. Thus each side of the strip is tin plated. An example of a suitable tin electrolyte is as follows:

V Gms./liter Stannoussulphate -130 sulphuric acid 3-6 Aloin 5 Succinic acid 1-2 Other acids `lnay be used than suceinic acid, such as I nalic acid. lactic acid, diphenyl sulphonated acid, hydro-lluosilicic acid and cresol sulphonic acid, or phenol sulphonic acid. Other suitable tin electrolytes may also Vbe used for electro-depositing the tin. s

The amount of tin4 deposited may be varied in accordance'with the use to which the product is to be put. In general, the weight of the deposit may be varied from one-quarter pound to three poundsoftinperbaseboxwhichisacoatingor deposit upon each side of the product of from 00015" to .00018" thick.

After leaving the tinv plating bath, the strip is waterrinsedinatank andmayalsobedried, if desirable, in heat chamber 31 from which thf strip `stock is drawn onward by pulling drums 38 and from the latter delivered to the Vsubsequent .als have, in most cases, va white or non-metallic appearance, yand in some cases are objectionably soft, both of which characteristics are objectionable toithetradefwhichjmakes useof plated strip steel stockiniaterial-forrworking up" into a greatv variety of products by such operations as stamping, deep-drawing, etc. .It is also desirable to alloy the `different metals to one another. `By the following steps non-ferrous coatings are given the desired hardness. an alloy .is formed, and the coatingis given the required bright metallic appearance, `so that it looks like buied vnickel or bufed stainless steel. y

-Describing what is shown in Fig. 4 oi' the drawings, the plated strip stock is passed through a heater lli which subjects 'the strip to a temperature just below the melting lpoint `of kthe lastplated non-ferrous coating on the strip stock Il.

In practice, I use temperatures ranging from five to twenty-five degrees F. below the melting point. Such heater as shown is electrical and includes a chamber within which are two sets of copper rolls 4I, each set being in pairs, one above the other, and the two sets being spaced apart in the direction of travel of the strip horizontally through the chamber of the heater 4|).

In the heater 40 the strip is heated in a reducing atmosphere by electrically heating to a temperature just below the melting point of the last deposited coating. This acts as a pre-heating step ahead of the heater and permits the plated coatingv to be quickly melted and smoothed and alloyed by the action of the reducing rolls I2 in heater I4. The temperature in heater M is above the melting point of the last coated metal. 'I'he contact between the strip and rolls I2 is for only a short interval of time and due to the rolling action of the heater rolls I2, the coating is smoothed and fused as it passes between the rolls 42 and solidifes as it passes out of heater 4I. The strip then is cooled in the cooling bath l5.

I nd that a highly lustrous coating may be produced if the temperature in the heater I0 is above the melting point` of the last deposited coating. Where the hot oil or low melting salt y f above is used in place of the electric heater 'the rollers 4| will be omitted; the strip is heated above the melting point of the last deposited coating and then quenched without coming in contact with guiding rolls. l

The copper rolls ll are connected in pairs with the opposite poles of a 12 to 18 volt D. C. variable speed generator, the two upper rolls of the two sets being, as shown, connectedto the positive side of the generator. Thus, by the heating of the rolls, the temperature above stated is produced and maintained in the chamber of the heater 40. Suitable means, not necessary to be described, are provided to control the temperature of the copperA rolls, 4i, such means comprising no part of my invention. 'l'.'he chamber 40, heated by the rolls 4 l is maintained at reducing atmosphere.

From the heater I0 the strip is passed (preferably through a closed conduit I3 between suitable guide rolls) to the heating means ll, which subiects the strip to a temperature above the melting point of the deposited :non-ferrous l.coating, :such heating lmeans including a `reducing stand which has 'upper'fand lower heat resisting yreducing rolls 42 :internally heated by electrical lunits, and 4between whida rolls I2 'the `strip is passed. The temperature of these rolls in practice .is from vte'n to `fifty F. above `the melting pointgof the `.Zlhe `rolls 42 contacting the melted coating act to smoothout and Isolidify it and form the alloy, "with its contiguous metal surface. f

The reducing rolls I2 are made of a metal ,which does not oxidize at 'the high ltemperatures to which they are subjected, and thus discoloration from oxidation is avoided. Buch rolls .may be .of a l,steel nickel chrome alloy that is heat resisting'. The heating means maybe electrical.

As a .resultoi 'the treatment or treatments by vwhich the plating on the strip is subjected to a melting temperature, kand while melted actedon by reducing rolls I2, I secure the results herein before set forth of giving the desired metallic luster to the non-'ferrous coating and the production yof an alloy 'between the metal layers.

After leaving lthe rolls 42, the strip is cooled, as'

by being passed through ya tank II containing oil or water at a temperature between 60 F. and

The nished product is wound into a roll upon a drum or reel I6 driven by a variable speed motor in order to compensate for the increasing diameter of the roll or coil.

The plating accomplished by the process exemplied in Figs. 1, 2 and 3 secures results satisfactory for many uses, without carrying the process further. However, better results are secured for Asome uses by the proper selection of the metal to be first plated on the strip stock Il, at I6, and continuing the process inaccordance with the treatnent shown and described with respect to Fig.

Of course, a number of strips, Il, may be simultaneously subjected to my process by being run through the apparatus side by sidebut not in contact with one another, and may have dimensions of from V4 inch to 84 inches in width, and from 1rooo inch to V4 inch in thickness, and a. length so great, sometimes several thousand feet long, that, for convenience in handling, it is wound into a coil.`

It will, of course, be understood that where, because of limitations of space, it is not possible or practical to have the 'above-described process run continuously without a break, the strip stock may be` wound on reels following each of the draw-drums 2|, 28, and 3l, as indicated in dotted lines at 50 and 5| in Figs. l and 2 or at any other convenient point in the process. A fully wound reel is then placed on an unreeling stand 52 (as in Fig. 2) at anybreak in the process so strips of great length are employed.

The tin-plated stock produced by the above process is superior to any hot tin coated strip or stock or any electro-tin-plated stock or sheet produced by known processes, yet is cheaper to produce. 'I'his is true because the plating can be um mmm .mmmwsmm mmfmmmd L Ff .m .us

s m Mmmm s u www s s m s mm was n smi s m sss mm W use@mmssm www m mmmm new msm mmm m s www M sm ,m xmmmmsdmhmm mmm M m m msmmmmmdmm Mmmm@ um mgm? msm s me? Mmmssmmmmmmm mmmmmmmmwwmmmmm mmsmmsmmm mmmwmmsmsmsl rmsmetnoddeumsumsea'unun lam-by ma n mm mm w w me www m e Mmmm s m ms s mm JOHN 8. NACHTLEAN andcopper controlling of said alloy laver by controlling ing atmosphere to a temperature 5a of 1950?. to provide at least three sisting of the strip steel. an alloy and copper 55 'between 000015" and 00018" side of the thus-plated heat-treated then heating the tin plated strip in atmosphere to a temperature at least as clean steel strip; then heating the thus-plated cobalt. tungstemandirondirectlyuponeachsideota temperature chromium um then hea'ung :ne then neaung the ums-plated strip controllingthethicknemotsaidallo! 'heit-Mspm -layer by controlling the heating temperature:

then electroplatin a. tincoatingbetweenml" Y and 0018" thick upon each side of the thus- V`perdirectlyllllllllelwllside0fU- plated heat-treated strip tinplatedstripinar'edueing-atmomheretoa temperature atleastashilhasthemelting point oitinwherebyatincoetlngalloyedtotbepreviously plated heat-treated strip is secured.

2.In amethodotcoatingstripsteelwithtin the steps of'electroplatlng a thin coating consist temverahlre then electmplatins a inge'ssentlally or ametalselectedtrom the class consisting of copper, nickel strip in a reducing atmosphere to a not in excess of 1950 layers; consisting'of thestrip steel .an alloy of the'steel and plating metal. and the plating 

